We used to have them. Devices so simple anyone with a hammer could fix. Maybe not open source as we understand it today, but rather - trivially reverse engineerable, often with schematics included. Most complex would be rewiring the motor on a washing machine. Did their job fine, but you can't sell them forever, so more complex devices were introduced. Nowadays motorcycles would probably be the closest equivalent, they're often very simple to work on.

There are freely available plans for all of those things. They are just more primitive than what you have in mind.